The present disclosure is directed to a composition and a method for forming polyamides and amidoamines from selectively modified amines. More specifically, the present disclosure is directed to polyamide curing agent compositions formed from selectively modified amines and epoxy-amine compositions.
Polyamide curing agents are utilized extensively in many markets for epoxy curing agents including coatings, adhesives, composites, and flooring applications. Polyamide curing agents are comprised of the reaction products of dimerized fatty acid (dimer acid) and polyethyleneamines, and usually a certain amount of monomeric fatty acid which helps to control molecular weight and viscosity. “Dimerized” or “dimer” or “polymerized” fatty acid refers, generally, to polymerized acids obtained from unsaturated fatty acids. They are described more fully in T. E. Breuer, ‘Dimer Acids’, in J. I. Kroschwitz (ed.), Kirk-Othmer Encyclopedia of Chemical Technology, 4th Ed., Wiley, New York, 1993, Vol. 8, pp. 223-237.
Dimer acid is typically prepared by the acid catalyzed oligomerization under pressure of certain monomeric unsaturated fatty acids, usually tall oil fatty acid (TOFA), though sometimes other vegetable acids such as soya acid or cotton acid are substituted. Commercial products generally consist of mostly (>70%) dimeric species, with the rest consisting mostly of trimers and higher oligomers, along with small amounts (generally less than 5%) of monomeric fatty acids. Common monofunctional unsaturated C16 to C22 fatty acids also employed in making polyamides include tall oil fatty acid (TOFA) or soya fatty acid or the like.
U.S. Pat. No. 3,519,582, which is hereby incorporated by reference in its entirety, discloses benzylated TEPA based poly amide in example “Hardener E.” U.S. Pat. No. 3,519,582 discloses that the benzylation is with benzyl chloride, which results in a non-selective benzylated amine. In addition, the benzylated product of the U.S. Pat. No. 3,519,582 includes undesirable byproducts containing chlorine that must be removed prior to subsequent use.
U.S. Pat. No. 7,473,806, which is hereby incorporated by reference in its entirety, discloses polyalkylene polyamines that are reacted with styrene. The resulting amines are benzylated and can be used to prepare some (poly) amido amines having properties suitable for use as an epoxy curing agent. However, the product of the U.S. Pat. No. 7,473,806 suffers from the drawback that the styrenated product was not heat stable and that a retro reaction takes place during the manufacture of a polyamide.
Several methods for preparation of (poly) amido polyamine and their use as curing agents for epoxy resins are known. For example, U.S. Pat. No. 2,705,223, which is hereby incorporated by reference in its entirety, describes epoxy resins cured with polyamides based on polymeric fatty acids and polyethyleneamines. European Patent Document EP 134,970, which is hereby incorporated by reference in its entirety, describes similar polyaminoamides. British Patent GB 2,031,431, which is hereby incorporated by reference in its entirety, discloses epoxy resins cured with mixtures of high molecular weight polyoxyalkylene polyamines and N,N′-bis(3-aminopropyl)ethylenediamine.
As a results of environmental regulations, and also as the need to reduce solvent levels in coatings has been perceived by coatings manufacturers and their customers, there has been a need to reduce the viscosity of the binders employed in coatings, and epoxy based coatings are no exception. However, in currently known products, as the viscosity decreases, it is generally found the amine hydrogen equivalent weight (AHEW) also decreases.
Epoxy resins are also available in many viscosities. A commonly employed epoxy resins are those based upon the diglycidyl ether of bisphenol-A (DGEBA), and higher molecular weight oligomers prepared by the advancement of the DGEBA with additional bisphenol-A. Such resins are usually difunctional or slightly less than difunctional, and characterized by their epoxy equivalent weight (EEW). Thus, bisphenol-A derived epoxy resin with an equivalent weight of 180 has a viscosity of about 8500 mPa·s (8500 cP). Slightly increasing the EEW to 190 increases the viscosity to about 12,000 mPa·s (12,000 cP). At an equivalent weight of 300 or so epoxy resins partially crystallize at a fairly rapid rate to a semi-solid and above an equivalent weight of about 400 they are solids, and thus their viscosities cannot be measured at room temperature.
In the formulation of coatings, it is frequently advantageous to employ higher molecular weight epoxy resins, such as those with equivalent weight of 450 to 550 (known in the industry as Type I resins). High molecular weight resins dramatically decrease the dry-to-touch time of the coating. Furthermore, higher molecular weight epoxy resins yield more flexible and impact resistant coatings than do lower molecular weight epoxy resins. Unfortunately, the high viscosity of the higher molecular weight epoxy resins requires the use of high levels of solvent in order to achieve a suitable application viscosity.
New regulations require reduced amounts of solvents in the formulation of the coatings as well as low emissions values during the life time of that coating. Local regulations in the U.S., Europe, Asia and elsewhere illustrate the desire that low viscosity is very important, where it is desirable to develop paints and coatings with <100 g/l VOC. Also lower viscosity means that the manufacturer can increase filler content of the system and thus decrease the cost of the coating formulation.
Improvements desired in the art of polyamide curing agents include low emissions, lower viscosity, little or no induction time, transparent mix with the epoxy resin that can be formed in an economical process that does not suffer from the drawbacks of the prior art. In addition, further desired features of the epoxy product include improved surface appearance, when applied under adverse conditions, good gloss and hardness development.